1. Field of the Invention
This invention relates to a confocal scanning microscope, which is of the transmission type wherein light, which has passed through a sample, is detected. This invention also relates to a scanning microscope provided with an improved mechanism for scanning a sample with a light beam. This invention also relates to a novel scanning mechanism for use in a scanning microscope.
2. Description of the Prior Art
Optical type scanning microscopes have heretofore been used. With the scanning microscope, a light beam is converged to a small light spot on a sample, and the sample is two-dimensionally scanned with the light spot. The light beam, which has passed through the sample during the scanning, or the light beam, which has been reflected from the sample during the scanning, is detected by a photodetector. An enlarged image of the sample is thereby obtained.
As one type of the scanning microscopes, a confocal scanning microscope has heretofore been proposed. With the confocal scanning microscope, a light beam is produced by a light source and is condensed to a light spot such that an image of the light spot is formed on a sample. Also, a point image of the light beam, which has been radiated out of the sample, is formed and detected by a photodetector. The confocal scanning microscope is advantageous in that no pinhole need be located on the surface of the sample.
Basically, the confocal scanning microscope comprises:
(i) a sample supporting member on which a sample is supported,
(ii) a light source which produces a light beam,
(iii) a light projecting optical means with which an image of the light beam is formed as a small light spot on the sample,
(iv) a light receiving optical means with which the light beam radiated out of the sample (i.e. the light beam, which has passed through the sample, or the light beam, which has been reflected from the sample) is condensed, and an image of the condensed light beam is formed as a point image,
(v) a photodetector which detects the point image, and
(vi) scanning mechanism for scanning the sample with the light spot in a main scanning direction and a subscanning direction.
In general, a pinhole plate is located on the upstream side of the photodetector in order to block a halo occurring around the point image and light scattered from the sample.
Confocal scanning microscopes are classified into a reflection type wherein a light beam, which has been reflected from a sample, is detected and a transmission type wherein a light beam, which has passed through a sample, is detected. Examples of the transmission type confocal scanning microscopes are disclosed in Japanese Unexamined Patent Publication Nos. 62(1987)-209510 and 63(1988)-306414.
The conventional confocal scanning microscope utilizes one of the following scanning mechanisms:
(1) a mechanism which two-dimensionally moves the sample supporting member, and
(2) a mechanism which two-dimensionally deflects the light beam by a light deflector.
However, the scanning mechanism described in (1) has the problem in that the sample flies out of its correct position when it is scanned quickly.
With the scanning mechanism described in (2), quick scanning can be achieved. However, in cases where the scanning mechanism described in (2) is employed in the transmission type confocal scanning microscope, the problems described below occur. Specifically, in such cases, a light beam, which is irradiated to a sample, is deflected, and the position, at which an image of the light beam which has passed through the sample is formed, changes in accordance with the position to which the light beam irradiated to the sample is deflected. Therefore, it is necessary for the photodetector to be moved in synchronization with the deflection of the light beam, which is irradiated to the sample. In cases where the photodetector is fixed, instead of being thus moved, a means must be used with which the light beam, which has passed through the sample, is deflected in synchronization with the scanning of the sample with the light beam. In cases where the mechanism for moving the photodetector or the means for deflecting the light beam, which has passed through the sample, is used, the confocal scanning microscope cannot be kept simple.
In order to eliminate the aforesaid problems, a novel mechanism has been proposed in, for example, Japanese Unexamined Patent Publication No. 62(1987)209510. With the proposed mechanism, the rear surface of a vibrating mirror, which deflects a light beam, is constituted as a reflection surface. The light beam, which has passed through a sample, is guided to the rear surface of the vibrating mirror and reflected and deflected thereby in ways which cancel the deflection of the light beam, which is irradiated to the sample. With the proposed mechanism, a photodetector need not be moved in synchronization with the deflection of the light beam, which is irradiated to the sample. However, with the proposed mechanism, many mirrors must be used in order to guide the light beam, which has passed through the sample, to the rear surface of the vibrating mirror. Therefore, the optical means becomes very complicated and difficult to assemble and adjust.
Also, in cases where the scanning mechanism described in (2) is employed, the problems occur in that it is difficult for the characteristics of the means for deflecting the light beam, which is irradiated to the sample, and the characteristics of the means for deflecting the light beam, which has passed through the sample, to be completely matched with each other. If the characteristics of both means do not completely match with each other, the light beam, which has passed through the sample, cannot be detected accurately.